The present invention relates to a process and an apparatus for the preparation of molded parts or objects from synthetic resinous materials, whereby employing an injection molding machine, the synthetic resin to be processed is subjected to deformation under pressure (pressure stretching) and/or pressure treatment with the use of a relatively high pressure, in a tool having one or several parting planes, or the preform during the cooling phase in the tool is subjected to such a treatment with the use of new or partially new mold cavities or the same mold cavity.
A process is already known from DE-OS No. 28 56 580, wherein a structure-forming process is carried out by means of a special pressure deformation during cooling after the initial molding or initial deformation, or is carried out in a separate work process. In this process, the initial material is an extruded, cast or injection molded semi-finished product, and compression deformation is effected. It is one of several disadvantages of the process that the molded parts formed are not dimensionally stable as a function of their external configuration and thickness and/or that they may contain defects (for example, breaks of the outer skin).
Furthermore, this pressure-forming process cannot be applied to molded parts having a projected area in the direction of the movement of the forming die which is larger than the surface of the die.